1. Field of the Invention
The present invention relates to a communication system and a communication apparatus.
2. Description of the Related Art
A network interface card (NIC) has conventionally been used for enabling a communication apparatus to communicate with other communication apparatuses via a network such as a local area network (LAN).
Ethernet® is popular as a representative network standard. A NIC compliant with the Ethernet® standard can perform communication by selecting one of a plurality of communication speeds of 10 Mbps, 100 Mbps, and 1000 Mbps.
Power saving has been required of the communication apparatus. In this regard, for example, Japanese Patent Application Laid-Open No. 2001-154763 discusses a technique for saving power by reducing a communication speed of the NIC when the communication apparatus operates in a power-saving mode.
To achieve more power saving, Japanese Patent Application Laid-Open No. 2007-276341 discusses a technique for cutting off power supplied to a part of the communication apparatus when the communication apparatus operates in the power-saving mode.
As a recent network related technique, a virtual local area network (VLAN) has been popular. This VLAN technique virtually divides a plurality of computer terminals physically connected to a network using a network device such as a switching hub into a plurality of groups (virtual network) to manage the groups as they belong to different LANs.
The VLAN technique includes a dynamic VLAN technique. In the dynamic VLAN technique, the switching hub virtually divides a plurality of computer terminals into a plurality of groups to manage them based on information (e.g., media access control (MAC) address) obtained from each of the plurality of computer terminals connected to the switching hub.
Consideration will be given to a case where a communication link with the switching hub is cut off in the communication apparatus connected to the switching hub compliant with the dynamic VLAN technique. In this case, to reconnect (link-up) the communication link with the switching hub, the communication apparatus has to transmit information such as a MAC address again to the switching hub.
It is because the switching hub compliant with the dynamic VLAN technique has determined that the computer terminal having its communication link cut off no longer belongs to (participates in) the VLAN when the cutting-off of the communication link is performed. To participate in the VLAN configured by the switching hub, the communication apparatus has to transmit information such as a MAC address to the switching hub.
In this regard, Japanese Patent Application Laid-Open Nos. 2001-154763 and 2007-276341 give no discussion about the dynamic VLAN technique. Thus, the techniques discussed in these two documents cannot simultaneously achieve power saving of the communication apparatus and complying with the dynamic VLAN.